A mold that can be separated into an upper mold and a lower mold is used in manufacturing golf balls by injection molding or compression molding. In such a mold, the location of the parting line, where the upper mold and the lower mold are separated from each other, on the surface of the ball is critically important. Therefore, the location of the parting line is selected in consideration of various aspects, including ease of arranging dimples and preparing a mold, designability, etc. One possible arrangement is that a parting line is formed along the equator of the cavity, and no dimples are disposed on the parting line. This arrangement allows a parting line to be easily formed; however, because dimples are disposed avoiding the parting line, the space between dimples having the parting line in between becomes unduly large. This adversely affects the designability. In an alternate method, the dimples are formed so as to lie over the equator of the cavity and the parting plane is formed along the peripheries of the dimples. In this method, the dimples can be closely arranged regardless of the location of the parting line. Therefore, although the formation of the parting line is difficult, good designability can be achieved in this arrangement.
However, as disclosed in Japanese Unexamined Patent Publication No. 1998-179808, the arrangement in which dimples are disposed so as to lie over the equator of the cavity is not desirably employed in recently used golf balls having a Shore D hardness of less than 60, in particular when a soft cover material, other than ionomer resin, is used (when an ionomer resin having a low hardness is used, the arrangement is also undesirable). Grinding may not be successfully conducted when such a soft cover material is used because of the too soft burrs formed, or may result in a rough ground surface.
When a mold separable into two parts is used, the resulting golf ball has burrs on the parting plane at which the mold is separated into an upper mold and a lower mold. Such burrs need to be removed by grinding, etc. When a parting line is formed along the peripheries of dimples which lie over the equator, burrs are formed along the peripheries of dimples. However, as shown in FIG. 9, a burr 100 formed on the periphery of dimple may fall into the dimple 200 when grinding is conducted in the direction shown by the arrow X to remove the burrs. If this happens, the burr 100 is hidden in the dimple 200 and may not be removed. (Note that, burrs are usually formed in a wall-like shape along the space where an upper mold and a lower mold come into contact; however, in order to schematically illustrate the status of the burrs when cut, FIG. 9 shows a cross-sectional view in the vicinity of the ball surface, and the cross section of the burr is illustrated as triangular.)
An object of the present invention is to provide a mold having a parting line along dimples. Using such a mold makes it possible to manufacture golf balls from which burrs can be successfully removed. Another object of the present invention is to provide golf balls manufactured using such a mold.